api 936 refractory under load refractory consultancy refractory industry american petrochemical institute testing & insoection fertilizer glass steel petrochemicals minerals refractory reversible thermal expansion thermal expansion thermal shock abrasion test creep refractory raw materials third party test refractory testing material qualification petrochemical abrading media 65 psi air pressure sic astm c704 refractory abrasion abrasion resistance
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